Process of coating porous articles



March 17, 1942. A|... M. BRlGl-IT PRocEss oF comme PoRoUs ARTICLES FiledNov'. 1-, 1958 I Patented Mar. 17, 1.942

2,276,685 PROCESS or CoA'rING PoRoUs ARTICLES Elvin M. Bright, M.Wallace,

Dayton, Ohio, assignor to John Cincinnati, Ohio, as trustee ApplicationNovember 1, 1938, Serial No. 238,215

1 Claim.

This invention relates to coating of articles and more particularly tothe coating of articles having a porous surface, such as articles madefrom wood or the like, or molded articles made rom a porous materialsuch as sawdust and other porous moldingmaterials.

An object of this invention is to provide a mask for a portion of thearticle to be coated.

Another object of this invention is to provide a priming coat forming abond between the surface of the article to be coated and the outercoating.

Another object of this invention is to provide a ller to be applied overthe priming coat, so as to smooth irregularities in the wood or thearticle, so as to present a uniform, flat or even surface. e

Another object of this invention is to provide a priming coat whichAnother object of this invention is to impreg- .nate wood with'nitrocellulose material.

Y Another object of this invention is to providev a coating for anarticle havng a porous, irregular surface, which coating is cheap,efiicient and at the same time presents a uniform, glossy surface.

Other objects and advantages reside in the construction of parts, thecombination thereof and the mode of operation, as will become moreapparent from the following description.

Referring to the drawing, i

Figure 1 is a perspective view of a shoe heel made from wood that is tobe coated with nitrocellulose material.

Figure 2 is a cross sectional view taken substantially on the line 2-2of Figure 1, to showi the several coatings.

Figure 3 is a schematic diagram showing the process of applying anitrocellulose coating or other coating to the article to be coated.

Numerous attempts have been made to provide a cheap priming coating forwooden or other porous articles to be coated, which priming coating isto function as a bond between the article to be coated and the outsidefinishing coating. None have been satisfactory when usinganitrocellulose coating or a nitrocellulose finish, which coating has notbeen bonded to the article but will form a bond between thenitrocellulose co ting and the` article to be coated.

the past, the air or solution will penetrate the pores of the wood, ex-

has formed a tight encasement without a bond.

between the article to be coated andthe outer nitrocellulose coating,whether this outer coating be applied in the form of sheets or byspraying or by dipping. Furthermore, when dipping the article intonitrocellulose solutions as used in of minute bubbles.

.found that by dipping the wooden article into gasses retained by thepores of the wood are liberated and will cause blisters underneath thecoating, resulting in a defective coating.y The elimination of this airhas been an unsolved problem. Before discussing the solution to thisproblem, a brief explanation will be made of a preliminary masking stepin the process.

Masking If the entirearticley is not to be coated, any portion may beexposed by masking such portion. Any suitable masking material that doesnot form a bond with the coating material and that has no objectionablefeatures as far as the article is concerned may be used. `If a woodenarticle is to be masked, it may be coated with either potassium orsodium silicate, more commonly known as waterglass The nitrocellulosematerial does not adhere to masking material. Furthermore, thewaterglass does not in any manner injure the wood later to be exposed.Although waterglasshas been disclosed for the purposes of illustration,any other suitable masking material may be used. l

Priming and bonding film or coating By dipping the article tobe coatedin a very thin solution of nitrocellulose material, wherein the greaterportion of the solution consists of the solvent for the nitrocellulosematerial, this thin pelling the air and the gases therein in the formFor example, it has been one-fourth pound of nitrocellulose materialdis.- solved in one gallon of Isotone, which is a trade name for asolution consisting of sixty percent acetone, twenty-five percentisopropyl acetate and fifteen percent anhydrous isopropanol, thatbubbles will form upon the outer surface of the article to be coated andeventually be liberated therefrom if the solution is not agitated over aperiod of twenty-five to forty minutes depending upon the condition ofthe wood, the shape of the body to be coated, the extent of the maskedarea, the quality of the material, the porosity of the article,etcetera. y

By agitating the solution in which the article is dipped, during thetime merged, the liberation of the gases is greatly accelerated.vThe-time is reduced to five to eight minutes, which is sufiicient timeto permit all of the air that will cause any deleterious effects to Thismaking step will now be described.

the waterglass that the mme is subbe expelled from the surface of thearticle to be coated.

In addition to the expulsion' of the air from the outer` surface of thearticle to be coated, the dipping ofv the article in this thin solutionof nitrocellulose material results in some of the nitrocelluloseYmaterial actually soaking into the pores of the wood, which has in thepast been considered absolutely impossible. If the dipping solutioncontained much more nitrocellulose material, the solution would be muchthicker, so as to form an exterior coating which would encase thearticle without expelling the air and without penetrating the pores ofthe wood. After the article is coated with this thick coating, some ofthe solvent would undoubtedly liberate some of the entrappved air,driving this air to the surface beneath the coating, where it forms abubble that is not released but may show up as a bulge in the finishedarticle. The thin lm covering the surface of the article .coated withthe extremely thin coating is impregnated or soaked into the surface ofthe wood, so as to form a. rigid bond with the article. This primingcoat is permitted to 'dry partially in the open air, without anyparticularly deleterious effect, as the coating is so thin that there isnot sufflcient thickness to house or enclose deleterious gas bubblesusually formed in nitrocellulose coating from rapid evaporation of thesolvent when cured in the air.

Finishing coat or coating The finishing coating may include (a) a dippedcellulose coating either with or without the use of a filler coating;(b) a spray coating either with or without a filler coating, or (c) acoating formed by applying sheets from preformed sheets of cellulosematerial.

In view of the ller coating when used being applied first, theapplication of the filler coating will now be described.

Filler coating Heels formed from Wood or other porous material usuallyhave some of the grains exposed, leaving rough surfaces. Even though thewood may appear to have a highly polished surface before the applicationof the priming coating, the l surface after being primed usually getsrough,

' due to the inherent structure of the material of the article.Therefore, it is necessary either to refinish the surface or to use aller coating to eliminate the irregularities. The former is notsatisfactory for the reason that it is impractical to polish a moistsurface and the cost is prohibitive. In the next place, if the primingcoating were permitted to harden to permit finishing, the purpose of thepriming coating would be partially defeated, as it does not form a goodbond where the outer film has been removed.

A ller coating may be applied by dipping the article into a liquidincluding a suitable comminuted inert filler material suspended innitro- .cellulose material dissolved in a suitable solvent. Comminuteddiatomaceous earth has^been found to give excellent results as an inertfiller material.

Due to the surface tension of the nitrocellulose material when it iscured, the filler coating has a tendency to fill the pores and the grainofthe Wood, so as to completely conceal the underlying material. Thiscoating may be cured by the process disclosed in my Patent No. 2,130,225granted A Sept. 13, 1938, which process includes the steps of cyclicallydipping or submerging the freshly coated article into a solution havingan attraction for the solvent used in dissolving the nitrocellulosematerial, in which solution the nitrocellulose is substantiallyinsoluble, then subjecting the article to a gaseous medium saturatedwith fumes from the solvent used in dissolving the nitrocellulosematerial.

If nitrocellulose material were used without having added thereto ai-lller material, the shrinkage would force the nitrocellulose materialinto the dips or detailed'low and high areas of the article. By addingthe ller material, it functions to' offset 'the deleterious shrinkage ofthe nitrocellulose material. This filler material prevents the free fiowof the nitrocellulose material. It actsas a buffer or impedance to thefiow of the nitrocellulose material. Therefore, the outer surface of thecured filler material has substantially the same contour as it hadimmediately after the article was removed from the dipping solution whenthe outer surface was smooth due to surface tension of the liquidcoating material. However,- the cured surface of the filler coatingdoes' not have .the desired gloss and texture. That` being the case, itis necessary to add a finishing coating that acts as a veneer plasticply coating.

After the filler coating, which may include the desired pigment'or dye,has been applied and cured sufficiently, the final flnishing coating maybe applied.

For the purposes of illustration, it has been found that as a fillercoating, two and one-half pounds of nitrocellulose material dissolved inone gallon of Isotone having added thereto threefourths pounddiatomaceous earth and a suitable pigment or the like, producesexcellent results. Any other suitable filler material may be used.

Finishing coating Removal of coating overlying mask When coating sucharticles as wooden shoe heels, it is necessary to remove the coatingfrom the top of the heel and also from the bottom. It has been foundthat by masking the top and the bottom of the heel, as described above,by a suitable material such as waterglass, the priming coating and thesubsequent coatings will not penetrate the wood covered by this maskingmaterial. Thus, after the article has been coated, thenitrocellulosematerial extending across the top of the heel and across the bottom ofthe heel may be cut away and removed bodily, so as to leave the woodexposed. This process-will now be described as ppllied to the coating ofa ladies wooden shoe In the drawing, the reference character I0indicates a heel of a ladies shoe, which has been turned from Wood orformed lfrom a plastic including sawdust, which heel is rough, due tothe grain in the Wood, and therefore must be coated, so as to fill thegrain of the Wood. The top sur- -face l2 of the heel and the bottom,which has not been shown, must have the Wood exposed i be satisfactory.

after the heel has been coated. I'hat being th case, the top surface ofthe heel andthe bottom thereof are rst coated with potassium or sodiumsilicate, more commonly known as waterglass. This has been shownschematically by the first square shownjin Figure 3. After the maskingcoating has been applied over the surfaces to be exposed, theheel isdipped into a thin nitrocellulose coating ld, as described above, andpreferably while the solution is agitated. The solution is agitated frombelow the liquidlevel Aand preferably below the lower. level of the heelby a controlled movement. This movement -should cause the liquid in thevicinity of the submerged article to have an upward movement so as tosweep upwardly the bubbles forming on the surface of the article. Thissweeping action of the bubbles causesI these bubbles to rise to thesurface of the solution. Any suitable agitator causing the solutionto-have the desired eddy currents may be used.

.This priming coating is permitted to dry in the air for a short periodof time. However, this coating should not be permitted to set or harden,as it is very desirable that the subsequent coating IS, which mayconsist of a ller material and Y nitrocellulose material dissolved in asuitable solvent as' for example Isotone, be applied before the primingcoating 'has hardened, that is, while it is moist, as the bond betweenthe priming coating and the iiller material would then dipping thearticle into a solution consisting of nitrocellulose material dissolvedin Isotone having added thereto diatomaceous earth and preferably asuitable pigment.

coating solution.

This nal coating solution may contain a pigment, or it may be clear.coating the nished article has greater depth to it. Whether or not apigment is added to this coating depends entirely upon the condition ofthe ller coating and the'requirements of the finished article. Thiscoating I8 preferably con- By providing a clearaevaese c.

Y This s olvent softens be more effective. The ller material may beapplied by sists of nitrocellulose material dissolved in Isotone,havingthe desired thus coated is again subjected to the curing, the sameas already described and as fully shown in my aforementioned patent.

After the nal coating has been cured, the ends subjected to a clickingmaof the heel maybe chine, so as to remove the coating materialoverlying the masking material, which coating material isjeasilyremoved, as it does not adhere to the waterglass. The article is nownisned and ready for use.

AlthoughaI heel hasbeen of illustration, dippedcan be subjected to theprocess described above.

used for the purpose Spray coating For some types of usage, a cheapercoating may Instead' of applying the 311er coating and a nishingcoating, a coating may be sprayed directly upon the priming coating,

viscosity. The article any type of article adapted to be mterial inwhich spray coating adheres to the priming coatt5 'with the moistcoating forms a ller coating Application of nitrocellulose sheets Forsome types of work it maybe desirable to apply sheets of nitrocellulosematerial directly to the article after it has been primed. Isotone orany other suitable solvent is preferably applied to the inside of thesheet to be applied to the article. the side of the sheet coming incontact with the moist priming nitrocellulose material that is saturatedinto the outer surface of the article to' be coated. The moist innerside of the sheet coming in contact a homogeneous union, so that theimpregnated priming coating and the outer applied sheeting form aunitary structure. Thus, a coating may be formed from vapplied sheetsthat has the chaiacteristicsfof a unitary impregnated coating. Thepriming coating constitutes a bond between the article and the coveringsheet. Where the surface of the coated article is irregular, as forexample a shoe heel, the sheet is preferably first preformed into I theapproximate shape of the nished article,

by any method well known to thosev skilled in the art.

Although a shoe heel has been used as the article to be coated, theprocesses .of applying the 'coating are applicable to any other.suitable article. Instead of nitrocellulose material, any other suitablecoating material having characteristics similar to nitrocellulosematerial may be used, as for example de-nitrated nitrocellulose materialand other cellulose materials such -as i scribed, it wm be understoodthat within the purview of this invention, equivalents not excluded bythe prior art are included which are capable of carrying' out theobjects as disclosed and '.dened in the appended claim.

Having thus described my invention, I claim:

The method of 'bonding a nitrocellulose coating to a. wooden articleincluding the steps of masking the mrtions of the article later to beexposed Without a coating, dipping the masked article into a thinsolution consisting of nitrocellulose material dissolvedin a suitablesolvent so as to expel the air from the pores of the wood and so as toimpregnate the outer surface of the Wood with the nitrocellulosematerial priming lm, partially drying the priming nlm, applying bydipping the impregnated article While the priming lm is moist into asolution including nitrocellulose material dissolved in a suitablesolventhaving added thereto a lier material, c the coating. dipping thearticle into a nishing coating including nitrocellulose'materialdissolved in a suitable solvent and curing the nishing coating bycyclically dipping the article into a solution -havingan attraction forthe solvent used in dissolving the nitrocellulose which solution thenitrocellulose material is substantially insoluble, and removing the azone saturated with the fumes from the solvent used in dissolving thenitrocellulose material, so as ,to cure the coating, and bodily removing'the nitrocellulose material overlying the masking material.

ENDE M. BRIGHT.

coating of

